Vmca -red line
Vyse - blue line
It might be possible to lower the nose build up speed to then be able to climb away...so therein a reason to feather, though if you are at that kinda height to achieve that the aircraft should be above blue line.
If you are so low as to be below below line, I put forward that spending time worrying about feathering the engine is a moot point and you are better closing the throttles and preparing for the crash landing ahead.
From memory in my training it was something like 300ft close the throttles landing ahead, above that and blue line then feather, and when above something like 1500ft continue the drills for basic troubleshooting.
As for knowing the speed specific for the weight, again if memory serves, in a light piston it is only a variation of some 5knts.